The Earth Wire is Missing! - Can You Use Steel Conduit Instead?
In our Conlok conduit installation video, we explored the electrical continuity of the full electrical installation. In most electrical installations today, most circuits are wired with a dedicated circuit protective conductor (CPC). Do you have to include a CPC conductor when using a metal conduit?
We'll explore the use of steel conduit as an earth conductor and how it's applied to multiple circuits contained within the same conduit or trunking.
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👉 • CONLOK: Will You Ever ...
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🕐 TIME STAMPS 🕕
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00:00 Can I use steel conduit as a CPC
01:06 What can we use as a protective conductor
02:54 CSA is important
04:43 More than one circuit
06:35 Line conductor size (S)
08:14 k1 and k2 values
09:03 Table 54.5 k value for steel conduit
10:38 Calculation
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#efixx #electricians #conduit
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I was on a job in a garage a couple years ago . The conduit appeared ok but I was a bit sceptical. . On pulling in new cables I found the existing conduit under the concrete floor was In fact very rusty and as I pulled the old cables out they were very wet and stained by the rust. Moral of the story is unless you can see the whole length of the conduit don’t trust it for earthing.
Lots of good stuff there. My opinion is run a separate CPC in the conduit and the same for SWA and stop trying to save money at the design stage. A main reason is that it may work and be ok when first installed but what happens when some of the joints start to work loose or the conduit/SWA armour starts to carode/rust
The system should be periodically tested so that would be picked up on but I'm just being arguemnetative because I fully agree with you run the CPC
Love these videos and the way Joe explains them. Anything that simplifies and better explains the regs and their application is worthwhile 👍
Different terms with the NEC over across the pond. We no longer allow mechanical means from faulty connections. We run an equipment grounding conductor with every run and bond every box with a splice. Simple and redundant.
Thanks Joe. Brilliant video as always. Cheers Craig 🙂👍🏼
I served my time on the 14th edition that stated the containment must be electrically & mechanically sound. When the 17th came out a lot of young sparks were failing installations as the "CPC" was missing and some ran them and removed the earth leads from the back of the conduit box
The socket retaining screws will make the earth to the back box and hence the conduit.
I’d run the separate CPC just for good measure. I have never ran it any other way. When doing my 2365-2 they taught me that way so that’s the way I’m going to do it but never the less joe, amazing information you have provided
Good explanation Joe 👍
If I was doing my own workshop I'd work everything out and give it a go, but doing it for some one else running in a separate cpc is definitely more sensible.
Yeah we tended to lean that way on site as well. 😊
I never got taught on how to do this calculation at college so thank you. During my apprenticeship I just got told it’s fine for sockets to use the steel for the earth but never why in steel conduit. I never did though rely on this and always added that 2x1.5 or 2x2.5 earth in.
Bloody clever stuff Joe!! 👏 👏
Nah, just lots of reading! 😂
@@efixx that’s the problem they pass you from pillar to post and back again before you get the answer!! Top work men👍
The issue here would be the Zs values measured at the farthest point and the likely hood of an increase in resistance from corrosion or vibration etc . Just install a copper cpc and don't worry about it
Could use an RCD as you would with a TT install as they seldom meet the required Zs as well
@@paulmatthews5470 yes you could .
Have found corrosion reduces zs so I alway include a earth cable
@@bernardcharlesworth9860 reduces Zs ??? Surely increases Zs , decreases fault current ?
When I was taught this in college - it boiled down to one simple fact for me... when it comes to 20 & 25mm steel conduit. If you can fit the line conductors in the bloody pipe, it will always be a suitable earth.
Your comment made me chuckle, unless you got a paper thin conduit
This is handy for an EICR on older Installations intended to use the conduit for the CPC, a lot of electricians would automatically fail the installation based on no seperate earth
Fantastic video 👌🏼👍🏼
About 50 years ago I used to find a lot of gripfast conduit which used clamps to join fittings, the paint had to be scraped off to ensure continuity and it was wired in singles VIR cable. Guess that was from the 20s. Looks like conlock is the modern equivalent!
Using the new conlock conduit system and assuming all freshly cut conduit ends have been painted (to prevent corrosion) then wouldn't the conlock grub screw be the only true metal to metal connection...? So shouldn't this whole calculation be based around the CSA of the conlock grub screw..? Or am I missing a trick where the protective coating of conduit paint is actually conductive..? Your thoughts please..? Great video as always guys 👍🏼
Conduit zinc coated? If so that leaves the contact being the grub screw and a line contact at the opposite point from the grub screw. Also what torque are you using for that screw? Not convinced.
But with that grubscrew-fixed system, all it would take is one loose grubscrew, or a bit of corrosion etc. at the fixing point and suddenly you have no cpc.
Thats only the same as the first cpc connection coming lose (if a radial)
I suppose adding grounding straps at each join in the conduit could be mitigation against that, although if going to that kind of detil you might as well just add an extra earth wire.
Interesting topic. Most of the projects I've worked on over the years, the contractors have always used a separate cpc, as it's easier. However it's definitely worth bearing in mind situations where we can use conduit as cpc, especially if you find it when carrying out an eicr.
Yeah, we tended to run an extra CPC in steel conduit as well, quite interesting to see where the cut off point is for using 20mm conduit as the CPC too.
Using the conduit as the CPC is only done in big commercial jobs. Done in a big job I was at in the Middle East - to US standards which were more 1930s. Saves a lot of earth wire on a big job though. Quicker to wire up as one less conductor to manipulate dress and tighten up. Done a lot in ye olden dayes when copper was very expensive.
Using the new conlock conduit system and assuming all freshly cut conduit ends have been painted (to prevent corrosion) then wouldn't the conlock grub screw be the only true metal to metal connection...? So shouldn't this whole calculation be based around the CSA of the conlock grub screw..? Or am I missing a trick where the protective coating of conduit paint is actually conductive..? Your thoughts please..?
@@essdee9143 Great observation.
To be fair as an X electrical sub contractor, I have never once relied on any metal conduit or trunking for a CPC for two reasons that superseded all other considerations... 1, when you are on price work time is money and you simply don't have time to waist on another calculation.. 2, when a simpler solution already exists (ie running a separate CPC) then all you'll be doing is waisting time and money exploring anything else.. Real world electrics fellas..! However this is a very interesting topic, keep up the great work 👍🏼
If I remember correctly you can use metal conduit as an earth conductor really it’s no different to using pyro, but I think it’s would be better to run a separate earth lead , just to make sure Fantastic video as always Joe 👍👍👍❤️
Thank you sir.
When is the next live show? Is it tonight or next week ?
I have done a job a few months ago and the client wanted galvanized conduit, I wish that I had discovered this conduit system, it would have saved a lot of time threading the conduit. lol
This is an absolutely brilliant vlog . Very informative and helpful. I have never in the years used the conduit or trunking as the CPC but I would consider it. The only question I have is where the trunking enters the accessory/consumer unit/ dis board or whatever require special attention regarding cleaning off paint to ensure a proper long term connection. It’s a bit like the question of SWA gland tags not being used on a steel enclosure.
Good question, we'll do some digging. 😊
That’s a well good question… hope we get some good answers as normal back!
I have seen square metal trunking as the CPC with cable bolted to the trunking at the corners and tees. Seen one where the trunking was played about with, having the cable CPC left off. Big break in the CPC.
Sounds like a problem... 🤔
@@efixx Always check, that the trunking is linked by bolted conductors.
I served my time on the 14th edition and the regs stated the containment should be electrically & mechanically sound ie an earth. When the 17th came out there was young sparks failing an installation due to no CPC .
I did an eicr on a school years ago when I was an apprentice and the conduit was used as the cpc all the readings were better than expected due to the conduit and parallel earth paths of the metal fabric of the building Had the nic assessor out at one point and he was arguing saying our readings couldn’t be correct! The sparks I was working with ran rings around him😂
Doesn't the grub screw reduce the cross sectional area? It only makes contact that you can rely on on the tiny screw, not the whole conduit
I had the same thought. I certainly don't think that the contact between conduit and fitting in this sort of push-in setup should be relied on as a dependable connection.
There's also the the part being pushed against the back of the housing, but yes, the entire conduit is not the contact point.
so the CSA might be only 60/70%... earthing conduits is a must, but in my view always run in a earth also
@@jfbeam the painted part
While the CSA of the conduit itself is sufficient, what about at the joints? As the joints are held together by a set screw, do you need to calulate the area of said screw as that is like to be less than the area of a conduit?
I have used the SWA as a CPC before on very large cables, But only when forced to do so and never used conduit or trunking as one. Otherwise I run in a CPC every time! Having seen some conduit installs I would never trust them to be a earth personally.
Better to install copper cpc in the event of external fixtures been added later on , Bit like underfloor heating pipes now in plastic covered and aluminium layer inside ,after time on radius the lining will have wore away with aluminium in contact with water , future problems ,
at the consumer unit side of things would you connect the conduit to the earth terminal or no? or dont you need to because its fixed to the consumer unit?
The relatively cheap cost of a copper CPC versus the Court Appearance for Health & Safety failings makes economic sense for any professional
Is there no significant difference in resistance/impedance between the steel conductor and copper when making these calcs?
Great refresh from college 👍🏼😂 but definitely don’t get paid enough for all that lol
Interesting video, as always. To save people time measuring/calculating conduit/trunking CSA's, Table D5 of GN 1 gives the values for common sizes - simples😃
This bit of the regs seems crazily weak. The end-to-end resistance of runs must be very unreliable even if you manage to get a good reading at installation. This stuff gets knocked and there's ingress of dirt, corrosion, etc, all the time especially there steel conduit is specified. What's the point of getting the torque correct to the nearest 0.1Nm in a distribution board and then relying on a grub screw or on-site threading and attaching it to a 2m lever arm? I guess it would be ok for RCDs where the CPC is just needed to sink enough current to trip it, but where you're talking about equipotential bonding or relying on fault overcurrent to trigger protection you need your CPC to be treated with the same respect as line conductors (except that you can assume its loads are transient in terms of heating).
Perfectly fine in canada to use steel conduit as your cpc.
How do you ensure a low impedance ground connection to the surface mount boxes, they're usually painted inside and out but no one ever mentions removing the paint, do conduit fittings cut through the paint reliably? Am I overthinking it?
Remove the paint or don't use that type of box. Commonsense should tell you you shouldn't be making an electrical connection with a layer of paint in the middle - unless it is purposely designed as electrically conductive paint... You are allowed to think for yourself.
When I was first on sites we used the conduit and trunking as cpc but after a few years running a cable was specified. I can only assume it was down to the designers, the same muppets who wanted us to get 6 x 4mm singles round 20mm pipe bends. Real Fairy Liquid job that one. 🤣
😂 Having been on both sides of that fence I totally sympathise Christopher.
Old commercial buildings use the conduit/trunking as the CPC
Yup!
Yup and I work in a factory like that. Seen lots of missing trunking and corroded conduit. 😳 Always have put a separate CPC apart from large SWA's when installing.
If I was going to consider using the conduit for the cpc, I definitely wouldn't be happy with a small grub Screw making a secure connection and continuity. Crap system, much better job to thread the pipe. Quicker is definitely not better in this case.
Depends why you are using conduit surely? Mechanical protection? - frankly a slip joint would be fine. Electrical continuity? Whether CPC or to meet Tempest requirements, screwed seems much more robust.
I wouldn't personally. I've always used an earth wire and fly leads for armoured, even if it's in metallic. Pyro's a little bit differently as the outside is the earthing and it's connect at both ends for the earthing.
No . I think. 🧐🤔 I'll check the code
I know code allows it, but I hate seeing people "cheap out". All it takes is one loose screw to break the ground. Or a conduit being cut, or section of plastic being introduced to screw everything up. And of course, sparky's and inspectors never actually check. (I've seen lighting circuits where the conduit wasn't secured at couplers or boxes. Inspectors never climb into the ceiling and pull on things.)
That was how we used to do it,conduit was the earth. Waitrose supermarkets was the last place I used conduit as earth,their spec,that was 25 years ago. There was a specific tester for conduit earthing if I remember correctly.
How would you ensure that the conduit itself is connected to an earth?
Drill a hole into it.
What happens when you have dissimilar metals,say steel conduit and an alluminium box/enclosure. In this example crystaline corrosion will set in with even a little dampness. Do the regulations say anything about this?
It's called galvanic corrosion.
Where do you study to become an electrician in England? Do they accept foraigners? I'm from Argentina and looking for "new horizons".
Yes as long as you are pleasant.
@@leewinters606 and don't insist that the Falklands..................
that picture of the Bush into the box looks like a black plastic ring
I ve used plastic conduit for the earth before.
🤣🤣
🤣🤣🤣😁
I struggle to find pvc 20mm banjos though.. Or I would too 🤣👍
@@muzikman2008 wrap it around the thread of the male adapter derrr
@@noworriesnoproblems6382 good idea, I'll use that technique on my next high integrity earthing install 💡😂 maybe some pvc cement to hold it in place as a safety measure..
How are you connecting the steel conduit to the earth bar in CU?
Connect a fly lead using the banjos bolt and nut
@@reddie8130 I assume that can drop to 1.5mm if using 2.5mm rather than 6mm.
@@johnburns4017 you can’t mix and match the calculated CSA and selection. If you are using selection as the video, then you should use the same CSA as the circuit line conductors. In which case it would be 2.5mm to the socket earth terminal. If you used less then you would need to prove it by the calculation. Although in practice you will almost always be able to reduce it.
@@rossthompson1936 So using the conduit it would be min' of 6mm cross section area of the conduit. If mixing it with cable the minimum size of the CPC is the size of the conductor in the cable, say 2.5mm
@@johnburns4017 it’s important to remember what you’re trying to do. In the video the CSA of the cpc is to be selected rather than calculated. If you were using copper, it would be the same size as the line - 2.5mm. But here steel is being used hence the k1/k2 calculation, which says the steel must be 6mm min. But if you are connecting the conduit to the accessory earth it’s going to be copper. Hence 2.5mm same as the line as per selection. If you calculated instead both the steel and copper would be less. Therefore you’d probably get away with 1.5mm. But you started with selection and should continue to do so unless you make the calculations.
So really, for all likely sizes of conductor in a 20 or 25 mm steel conduit the conduit will be fine as the CPC...
Yur, the cable needs to get pretty maohoosive before it becomes non-compliant to use the conduit.
All very true no doubt....but not the kind of thing to spring on a chap in the morning with a sore head😄😄😄
🤦🏻♂️👍🏻
Soooooooooooooooo. Can we use the conduit as CPC or what
No flying lead one thing no earth is another ... I wouldn't rely on that now days when I find old systems like this I add an cpc personally
Don't you have to divide that figure by 8 due to poor conductivity of steel compared to copper like you would when using the armour of an SWA cable for your CPC?
Looks to me like the k2 value here factors in the lower resistance but I may be wrong.
This. 👆👍
@@efixxcool 😎
Use plastic sockets!In Europe it works,so why not in the UK?
We use metal where the environment demands it, mainly in commercial and industrial sites as it stands up to any potential damage from fork trucks etc, plastic would just smash. However there's is a increasing trend to install metal conduit and metalclad accessories within homes for aesthetic value (the industrial look).
@@seanthespark I have bin in lots off factories in the Netherlands and no metal sockets seen or installed!
Interesting to also watch this video: kzhead.info/sun/p8iKe9ejhX-Ela8/bejne.html by John Ward. Although, I personally (or professionally) wouldn't use that ConLock system if using the conduit as the CPC, only the traditional screw in type.
Would seem sensible to earth any metal trunking/conduit etc. anyway, whether or not there is a cpc. Back boxes are generally earthed and a cable could get snagged when passing it through the trunking/conduit, making it live.
If the conduit is the CPC would that snagged cable situation not then disconnect the protective device? 🤔
@@efixx Indeed, but if not earthed it would remain live (?) Is it not the equivalent of a water or gas bond? - even if it doesn't go fully into earth.
@@efixx Being pedantic here.....but you mean TRIP the protection device😁
My head hurts.
It is a bit heavy
Adiabatic equations or just run a cpc? Hmmm... Good practice to just run a cpc me thinks 🤭
? Pi x 8.63^2 = 233.98 and not 244.95???? Still, makes no difference to your proof that the steel conduit is plenty fine to be used as the CPC in this instance. (314.16 - 233.98 = 80.18 mm^2 CSA for the CPC...)
I do appreciate all the math and science that goes into cable calcs and one reg that that refers to another reg providing 2 other regs are met and they all satisfy another reg....🤨 Do you know what..... my time is better spent on the tools rather then at a desk with a calculator and 9 of my fingers in different pages of the reg book and its tables... Sorry but im just gonna buy a couple of coils of earth wire.... If you have a few guys in your company and one of them can do all the paperwork and calcs then crack on.... but if your on your own then you need to be earning the monies.... And beside the most important fact....Bar none is conduit , bushes, couplers nuts etc are absolutely a load of cheap crap.... and it dont matter where you buy it from... its crap, threads are very loose and surface areas on bushes are minimum as are gutter nuts..... you compare containment quality from late seventies early 80s to modern metalwork and your mind will be blown... British Standards must be getting brown envelopes from someone on a regular basis because quality has gone down the toilet... FACT... I wouldnt fancy a fault current being trusted down the conduit and accessories....
OK.
If the neutral & earth meet back at the transformer, why do you even need an earth.
LIKE WATCHING A DOG SHIT ON YOUR PATHWAY WHEN YOUR SITTING IN YOUR PANTS AND ITS PISSING DOWN WITH RAIN
If electricians did conduit tightly you got no problems,,with the size of the tube it'll always be big enough for use as earth,just don't do it like that anymore,same as not having flyleads to ceiling grids or radiators,not done anymore,different times.